Noncontact type IC card

ABSTRACT

The present invention relates to an electronic device that suppresses reduction in reception sensitivity and occurrence of distortion when IC cards are used while stacked. A loop antenna equipped on the IC card has up to four turns, and is designed so that one turn, for example, has a first linear portion, a first curved line portion, a second linear portion, and a second curved line portion. When two electronic devices having a first loop antenna and a second loop antenna, respectively, are stacked onto one another, the corners of the loop antennas do not overlap. For example, the corner formed by first curved line portion and the second linear portion of the first loop antenna is overlapped with the first curved line portion of the second loop antenna. The first and second loop antennas are shaped such that when two electronic devices are stacked, their respective loop antennas are superimposed in the opposite direction so that the corners are not overlapped and the amount of overlap as a whole is reduced. The present invention may be applied to an IC card for receiving/transmitting data under non-contact state.

TECHNICAL FIELD

The present invention relates to an electronic device, and particularlyto an electronic device for suppressing reduction of a receptionefficiency at maximum and performing the processing on the basis ofsignals having little distortion when data are written into or read fromplural IC cards under a non-contact state while the plural IC cards arestacked.

BACKGROUND OF THE INVENTION

Recently, non-contact type IC (Integrated Circuit) cards have beenpopular, and they have been introduced as common tickets totransportation facilities such as subways, buses, or ferries and forelectronic money systems, etc. The data writing/reading into/from the ICcards are carried out in the non-contact style on the basis of theprinciple of electromagnetic induction.

That is, in the non-contact IC card system, electromagnetic wave isemitted from a loop antenna having a reader/writer for writing/readingdata into/from an IC card, and the electromagnetic wave emitted isreceived by a loop antenna equipped in the IC card, wherebycommunications are made between the IC card and the reader/writer.

Further, in order to eliminate a load imposed on an IC card maintenancework, the IC card is provided with no battery, and thus it is designedto achieve required power from the electromagnetic wave received.Therefore, the IC card is required to receive electromagnetic wave asefficiently as possible.

In general, the IC card is equipped therein with a loop antenna 1 havingtwo or more turns of wire formed in a rectangular shape which is aslarge as possible as shown in FIG. 1. The loop antenna 1 receivessignals by resonating a resonance circuit with the carrier frequency ofelectromagnetic wave emitted from the reader/writer.

The IC card is basically used alone, however, there is a case where twoIC cards are used together with being stacked. For example, when a userpasses over a commuter pass zone and then gets off at a station out ofthe commuter pass zone, the user presents his/her commuter pass and aniO card (trademark) (it is assumed that each of the cards comprises anIC card) to a reader/writer while these cards are stacked in order toadjust the surcharge of the over-zone. At this time, the reader/writeror a non-contact IC card system connected to the reader/writerrecognizes the zone of the commuter pass thus presented, and thencarries out the processing of calculating the extra distance the userhas ridden, calculating the surcharge based on the extra distance of theover-zone and adjusting the account on the iO card.

Not only when one IC card is presented, but also when plural IC cardsare stacked, it is necessary that electromagnetic wave can beefficiently received so that each of the IC cards can operate desiredcommunication operations.

For example, when two IC cards each having a loop antenna 1 having theconstruction shown in FIG. 1 are stacked with the IC card placed face upwhile being perfectly overlapped with each other in the view from theupper side (when the two IC cards are stacked so that the top side ofone card faces the back side of the other card) as shown in FIG. 2, thelinear portions L1 to L9 constituting the respective sides of rectanglesof the conductor constituting the loop antenna 1-1 of one IC card areoverlapped with the corresponding linear portions L11 to L19 of the loopantenna 1-2 of the other IC card, respectively. At this time, theresonance frequency of the resonance circuit of the loop antenna 1-1,1-2 is reduced to the inverse of the square root of 2 (1/√2) of theresonance frequency when only one loop antenna 1 is provided (only oneIC card is provided).

That is, when the IC cards are overlapped, coupling occurs between theresonance circuits thereof. Therefore, the resonance frequency is equalto 1/(2π√(LC)) in the case of one IC card, however, it is equal to1/(2π√(L·(2C))=(1/√2)·1/(2π√(LC)) in the case of two stacked IC cards.That is, when IC cards are stacked, the resonance frequency of theresonance circuit of each IC card is displaced from the carrierfrequency of the electromagnetic wave by 1/√2, and the receptionefficiency is reduced.

However, for example when the carrier frequency of the electromagneticwave emitted from the reader/writer is equal to 13.56 MHz, by settingthe resonance frequency of the resonance circuit of each IC card to 17.5MHz higher than the carrier frequency in advance, the electromagneticwave can be received not only when only one IC card is used, but alsoeven when two IC cards are used while they are stacked so as to be facedin the same direction.

When IC cards are stacked while one IC card is placed face up and theother IC card is placed face down as shown in FIG. 3 (two IC cards arestacked while both the top sides thereof or both the back sides thereofface each other), both the linear portion L1 of the loop antenna 1-1 andthe linear portion L13 of the loop antenna 1-2, both the linear portionL2 of the loop antenna 1-1 and the linear portion L12 of the loopantenna 1-2 and both the linear portion L3 of the loop antenna 1-1 andthe linear portion L11 of the loop antenna 1-2 are respectivelybasically overlapped with each other, however, the overlapping style ismore complicated than that of FIG. 2.

The theoretical ground has not been necessarily clear, however, it hasbeen discovered from at least experiment results that the resonancefrequency is further reduced as compared with the case where IC cardsare stacked as shown in FIG. 2. As described above, the method ofsetting the resonance frequency of the resonance circuit to a valuehigher than the carrier frequency in advance in consideration of thecase where plural IC cards are stacked has such a problem that it canachieve a sufficient effect both when one IC card is used and when twoIC cards are stacked so as to be faced in the same direction as shown inFIG. 2, however, it cannot achieve a sufficient effect when two IC cardsare stacked so as to be faced in the opposite directions as shown inFIG. 3.

Further, there is a problem that when two IC cards are stacked,reception signals contain distortion.

DISCLOSURE OF THE INVENTION

The present invention has been implemented in view of the foregoingsituation, and has an object to prevent reduction in receptionefficiency and thus reduce distortion of signals received by designingloop antennas so that it is difficult to couple the loop antennas evenwhen IC cards are overlapped with one another in any way.

A loop antenna of an electronic device according to the presentinvention is characterized in that the loop antenna is shaped so thateven when plural electronic devices are stacked so that at least partsof the top sides thereof face one another or at least parts of the backsides thereof face one another, the conductors constituting the portionsof the loop antennas which are located in the neighborhood of thecorners of the electronic devices each having a substantiallyrectangular shape are prevented from being overlapped with one another.

The loop antenna may be designed to have a parallelogram shape orelliptical shape as a basic shape.

The basic shape of the loop antenna may be constructed as asubstantially annular shape by a combination of two straight lines andtwo curved lines while the two straight lines are disposed in parallelto each other.

The basic shape of the loop antenna may be constructed as asubstantially annular shape by a combination of two or four curved linesthat are different in shape.

A loop antenna of an electronic device according to the presentinvention is characterized in that one of two corner portions that aredisposed so as to sandwich the center line therebetween is disposed tobe close to the center line, and the other corner portion is disposed tobe far away from the center portion.

A loop antenna of an electronic device according to the presentinvention is characterized in that the loop antenna is shaped so thatthe line connecting two points of the loop antenna that are located atthe closest positions to the corners of the electronic device so as toconfront each other is coincident with a diagonal line of the electronicdevice having a substantially rectangular shape.

An information writing/reading device according to the present inventionis characterized by including reading/writing means for writing/readinginformation into/from plural electronic devices when the pluralelectronic devices are partially overlapped with one another, the pluralelectronic devices having loop antennas shaped so that when the pluralelectronic devices are stacked so that at least parts of the top sidesthereof face one another or at least parts of the back sides thereofface one another, the conductors constituting the portions of the loopantennas that are located in the neighborhood of the corners of theelectronic devices each having a substantially rectangular shape are notoverlapped with one another.

An information writing/reading method according to the present inventionis characterized by including a writing/reading step of writing/readinginformation into/from plural electronic devices when the pluralelectronic devices are partially overlapped with one another, the pluralelectronic devices having loop antennas shaped so that when the pluralelectronic devices are stacked so that at least parts of the top sidesthereof face one another or at least parts of the back sides thereofface one another, the conductors constituting the portions of the loopantennas that are located in the neighborhood of the corners of theelectronic devices each having a substantially rectangular shape are notoverlapped with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a loop antenna 1;

FIG. 2 is a diagram showing the overlap between loop antennas 1;

FIG. 3 is a diagram showing the overlap between the loop antennas 1;

FIG. 4 is a block diagram showing an example of the construction of anon-contact IC card system to which the present invention is applied;

FIG. 5 is a circuit diagram showing an example of the construction of IC13 of FIG. 4;

FIG. 6 is a diagram showing the shape of the loop antenna 1;

FIG. 7 is a diagram showing a signal transmitted from a reader/writer21;

FIG. 8 is a diagram showing a signal processed by an IC card 11;

FIG. 9 is a diagram showing a equivalent circuit when two loop antennas1 are overlapped with each other;

FIG. 10 is a diagram showing another shape of the loop antenna 1;

FIG. 11 is a diagram showing a state that two loop antennas 1 having theshape shown in FIG. 10 are overlapped with each other;

FIG. 12 is a diagram showing a signal to be processed by the IC card 11;

FIG. 13A is a diagram showing another shape of the loop antenna 1;

FIG. 13B is a diagram showing another shape of the loop antenna 1;

FIG. 13C is a diagram showing another shape of the loop antenna 1;

FIG. 13D is a diagram showing another shape of the loop antenna 1;

FIG. 13E is a diagram showing another shape of the loop antenna 1; and

FIG. 13F is a diagram showing another shape of the loop antenna 1.

BEST MODES FOR IMPLEMENTING THE INVENTION

FIG. 4 shows an example of the construction of an non-contact type ICcard. The IC card 11 is a battery-less type IC card having no batteryfor power supply. A loop antenna 1 constituting a resonance circuit incombination with a capacitor 12 receives electromagnetic wave (indicatedby a solid line) emitted from a reader/writer 21, converts theelectromagnetic wave received to an electrical signal and then suppliesthe electrical signal to IC 13. The inner construction of the IC 13 willbe described later with reference to FIG. 5.

A host computer 31 controls DPU (Digital Processing Unit) 41 of thereader/writer 21 to write predetermined data into the IC card 11 or readout predetermined data from the IC card 11. Further, the host computer31 processes the data which is input from DPU 41 and read out from theIC card 11, and displays the data on a display portion (not shown) asoccasion demands.

DPU 41 generates control signals for various kinds of control on thebasis of an instruction from the host computer 31 and controls amodulation/demodulation circuit 42. In addition, it generatestransmission data corresponding to the instruction and supplies the datato the modulation/demodulation circuit 42. Further, DPU 41 generatesreproduction data on the basis of response data from themodulation/demodulation circuit 42 and outputs the data to the hostcomputer 31.

The modulation/demodulation circuit 42 modulates the transmission datainput from DPU 41 and supplies the data to a loop antenna 43. Themodulation/demodulation circuit 42 also demodulates modulated wave fromthe loop antenna 43, and inputs the demodulated data to DPU 41. The loopantenna 43 emits the electromagnetic wave corresponding to the modulatedsignal input from the modulation/demodulation circuit 42.

Next, the specific construction of the reader/writer 21 and IC 13 willbe described with reference to FIG. 5. In this figure, themodulation/demodulation circuit 42 of the reader/writer 21 shown in FIG.4 is illustrated as an oscillator 42A serving as a modulation circuitand a demodulation circuit 42B.

IC 13 which is connected to a resonance circuit comprising the loopantenna 1 and the capacitor 12 of the IC card 11 has a rectifyingcircuit 61. The rectifying circuit 61 comprises a diode 71, a resistor72 and a capacitor 73. The rectifying circuit 61 rectifies and smoothensthe signal supplied from the loop antenna 1, and supplies apositive-level voltage to a regulator 64. The regulator 64 stabilizesthe positive-level voltage thus input, converts it to a DC voltagehaving a predetermined level and then supplies it as a power source to asequencer 66 and other circuits.

A modulation circuit 62 is connected at the rear state of the rectifyingcircuit 61. The modulation circuit 62 comprises a series circuit of animpedance element 81 and FET (Field Effect Transistor) 82, and it isconnected to the loop antenna 1 constituting a coil of the resonancecircuit in parallel. FET 82 is turns on or off in conformity with thesignal from the sequencer 66 to set a state that the impedance element81 is inserted in parallel to the loop antenna 1 or a state that it isnot inserted in parallel to the loop antenna 1, whereby the impedance(the load of the loop antenna 43) of the circuitelectromagnetically-coupled to the loop antenna 43 of the reader/writer21 through the loop antenna 1 is varied.

The signal which has been rectified and smoothened by the rectifyingcircuit 61 is supplied to a high pass-filter (hereinafter referred to asHPF (High pass-Filter)) 63 comprising a capacitor 91 and a resistor 92,and high-band components thereof are extracted and supplied to ademodulation circuit 65. The demodulation circuit 65 demodulates thesignal of the high frequency components input thereto and outputs thesignal to the sequencer 66.

The sequencer 66 has ROM (Read Only Memory) and RAM (Random AccessMemory) (both are not shown) therein, stores a signal (command) inputfrom the demodulation circuit 65 into RAM, analyzes the signal accordingto a program contained in ROM, and reads out data stored in the memory67 on the basis of the analysis result as occasion demands. Thesequencer 66 further generates a response signal to return a responsecorresponding to the command, and supplies it to the modulation circuit62.

Next, the operation of the reader/writer 21 and the IC card 11 shown inFIG. 5 will be described by taking as examples a case where informationis written from the reader/writer 21 into the IC card 11 and a casewhere information is read out from the IC card 11. The host computer 31controls DPU 41 of the reader/writer 21, and instructs the writing ofprescribed data into the IC card 11. On the basis of the instructionfrom the host computer 31, DPU 41 generates a command signal for thewriting, generates transmission data (writing data) corresponding to theinstruction and supplies the data to the oscillator 42A. The oscillator42A modulates the oscillation signal on the basis of the signal input,and supplies it to the loop antenna 43. The loop antenna 43 emits theelectromagnetic wave corresponding to the modulation signal input.

The resonance frequency of the resonance circuit comprising the loopantenna 1 and the capacitor 12 of the IC card 11 is set to the valuecorresponding to the oscillation frequency (carrier frequency) of theoscillator 42A. Accordingly, the resonance circuit receives the emittedelectromagnetic wave by its resonance operation, converts theelectromagnetic wave received to an electrical signal and then suppliesit to the IC 13. The electrical signal thus converted is input to therectifying circuit 61 equipped to the IC 13. The diode 71 of therectifying circuit 61 rectifies the signal input, and the capacitor 73smoothens the signal, and thereby supplying the positive-level voltagethereof to the regulator 64. The regulator 64 stabilizes thepositive-level voltage input, converts it to the DC voltage havingprescribed level, and then supplies the DC voltage as a power source tothe sequencer 66 and other circuits.

The signal which has been rectified and smoothened by the rectifyingcircuit 61 is supplied through the modulation circuit 62 to HPF 63 toextract high-band components, and the high-band components thusextracted are supplied to the demodulation circuit 65. The demodulationcircuit 65 demodulates the signal of the high-frequency components thusinput, and outputs the signal to the sequencer 66. The sequencer 66stores the signal (command) input from the demodulation circuit 65 intoRAM, analyzes the signal according to the program contained in ROM, andwrites the writing data supplied from the demodulation circuit 65 into amemory 67 on the basis of the analysis result.

When the command supplied from the demodulation circuit 65 is a readingcommand, the sequencer 66 reads out the data corresponding to thecommand from the memory 67. The sequencer 66 turns on or off FET 82 inconformity with the data thus read out. When FET 82 is turned on, theimpedance element 81 is connected to the loop antenna 1 in parallel, andwhen FET 82 is turned off, the parallel connection is released. As aresult, the impedance of the load circuit of the loop antenna 43 whichis electromagnetically connected through the loop antenna 1 varies inaccordance with the read-out data.

The terminal voltage of the loop antenna 43 varies in accordance withthe variation of the impedance of the load thereof. The demodulationcircuit 42B reads this variation to demodulate the read-out data andoutputs the demodulated data to DPU 41. DPU 41 properly processes thedata input thereto, and outputs the data thus processed to the hostcomputer 31. The host computer 31 processes the read-out data input fromDPU 41, and displays the data on the display portion (not shown) asoccasion demands.

FIG. 6 shows the construction of the loop antenna 1 installed in the ICcard 11 shown in FIGS. 4 and 5. The portions corresponding to the priorart are represented by the same reference numerals, and the descriptionthereof is suitably omitted. The loop antenna 1 shown in FIG. 6 has arectangular shape as a basic shape, and has four turns. The value of theinner angle θ of each of all the four corners is set to 90°−α in anyturn. That is, the inner angle between the linear portion L1 and thelinear portion L2, the inner angle between the linear portion L2 and thelinear portion L3, the inner angle between the linear portion L3 and thelinear portion L4 and the inner angle between the linear portion L4 andthe linear portion L5 are set to 90°−α. Here, the value of the constantα may be set to any positive or negative value other than 0.Accordingly, the respective linear portions are kept in non-parallelstate at each side of the rectangle. For example, at the upper side ofthe rectangle, the linear portions L2, L6, L10 and L14 are kept to benon-parallel to one another.

The terminals 14-A, 14-B are connected to IC 13. By designing the loopantenna 1 in such a shape, the linear portions of the loop antenna 1 arehardly coupled to one another (when viewed from the upper side, theoverlap portion of the linear portions is reduced) and thus thereduction in reception efficiency can be suppressed in both the casewhere the two IC cards 11 are stacked with being faced in the samedirection as shown in FIG. 2 and the case where thy are stacked withbeing faced in the opposite directions as shown in FIG. 3.

As a result, in any case where one IC card 11 is used, two IC cards arestacked with being faced in the same direction or two IC cards arestacked with being faced in the opposite directions, the receptionsensitivity enough for communications can be achieved.

Next, FIG. 8 shows the measurement result of a reception voltagereceived by an IC card 11 to which the loop antenna 1 as shown in FIG. 6is applied when a signal having a waveform as shown in FIG. 7 istransmitted from the reader/writer 21 to the IC card 11. In FIG. 7, theaxis of ordinate represents a transmission voltage (V), and the axis ofabscissa represents a lapse time (second). In FIG. 8, the axis ofordinate represents a reception voltage (V), and the axis of abscissarepresents a lapse time (second).

The voltage V1 of FIG. 7 and the voltage V2 of FIG. 8 have differentvalues, and the axes of ordinate of FIGS. 7 and 8 are different inscale. The measurement result shown in FIG. 8 is a measurement resultwhen two IC cards 11 each having a loop antenna 1 as shown in FIG. 6 arestacked with being faced in the opposite directions as shown in FIG. 3.

Even when a signal having a good waveform as shown in FIG. 7 istransmitted from the reader/writer 21 to the IC card 11, it is processedas a signal having a distorted waveform as shown in FIG. 8 at the ICcard 11. In order to discover the cause for the distortion, a schematicequivalent circuit to the IC card 11 as shown in FIG. 9 is considered.

In this case, it may be considered that two IC cards 11 are kept to bestacked and the IC cards 11 having the same construction are connectedto each other through a capacitor 101-1 and a capacitor 101-2. The innerconstruction of the IC 13-1, 13-2 is similar to the inner constructionof the IC 13 shown in FIG. 5, and it comprises the rectifying circuit61, the modulation circuit 62, etc.

The reason why the signal to be processed at the IC card 11 becomes asignal having distortion as shown in FIG. 8 when the signal having thewaveform shown in FIG. 7 is transmitted from the reader/writer 21 to theIC card 11 is associated with capacitance represented by the capacitors101-1, 101-2 which are induced by the overlap between the two loopantenna 1-1 (IC card 1-1) and the loop antenna 1-2 (IC card 1-2). Thedistortion can be suppressed by reducing the capacitance.

The capacitance represented by the capacitors 101-1, 101-2 is dependenton the physically overlapped portion between the loop antenna 1-1 andthe loop antenna 1-2. That is, as the overlap portion between the loopantenna 1-1 and the loop antenna 1-2 is increased, the capacitancerepresented by the capacitor 101-1, 101-2 is increased. Particularly inthe loop antenna 1 having a shape as shown in FIG. 6, the lines at theportions other than the linear portions L1 to L16, that is, at the fourcorner portions are in closer formation than at the linear portions. Ifthe loop antennas are prevented from being overlapped with each other atthe four corner portions, the capacitance represented by the capacitors101-1, 102-2 could be reduced.

Therefore, a loop antenna 1 having a shape as shown in FIG. 10 isconsidered. In the loop antenna 1 shown in FIG. 10, the portionscorresponding to the loop antenna 1 shown in FIG. 6 are represented bythe same reference numerals. In the shape of the loop antenna 1 shown inFIG. 10, two sides out of four sides comprise a substantially arcuatecurved line L1, L5, L9, L13, L17 and a substantially arcuate curved lineL3, L7, L11, L15 at the confronting position, and the remaining twosides comprise a linear portion L2, L6, L10, L14 and a linear portionL4, L8, L12, L16 at the confronting position.

In FIG. 10, IC 13 is connected between the terminals 14-A and 14-B (notshown), and the capacitor 12 is connected to IC 13 in parallel.

By setting the two corners out of the four corners to right-angle shapeand setting the other two corners to curved-line shape, as shown in FIG.11 the two loop antennas 1 are prevented from being overlapped with eachother at the corner portions at which the lines are closer to oneanother even when the two loop antennas 1 are overlapped with each otherwith being faced in the opposite directions, and thus the signalreceived can be processed as a signal having less distortion.

FIG. 12 is a diagram showing a signal to be processed in the IC card 11when a signal having a waveform as shown in FIG. 7 is received from thereader/writer 21 by a substantially one IC card 11 achieved by stackingtwo IC cards 11 equipped with the loop antenna 1 having the shape shownin FIG. 10 so that the IC cards 11 are faced in the opposite directions(that is, the IC card 11 including two loop antennas 1 overlapped witheach other as shown in FIG. 11).

Comparing the waveform shown in FIG. 8 and the waveform shown in FIG.12, it is apparent that the waveform shown in FIG. 12 has lessdistortion than the waveform shown in FIG. 8. When an IC card 11 isfabricated so that two loop antennas 1 are overlapped with each otherwith being faced in the opposite directions, the signal received can beprocessed as a signal having less distortion by designing the loopantennas so that the overlap portion thereof is reduced, particularlythe four corner portions are not overlapped. The shape in which the fourcorner portions are not overlapped results in reduction in the overlapportion as a whole.

As the shape of the loop antenna 1 based on the consideration that thefour corner portions (portions at which the line density is high) arenot overlapped may be used such a shape as shown in FIG. 13 in additionto the shape shown in FIG. 10.

The shape shown in FIG. 13A is a parallelogram, and the upper and lowersides in the figure are disposed in parallel to the sides of the IC card11.

The shape shown in FIG. 13B is set so that the two sides out of the foursides of the parallelogram shown in FIG. 13A are formed of curved linesand the sides of the upper and lower linear portions in the figure aredisposed in parallel to the sides of the IC card 11. The shape shown inFIG. 13C is set so that all the four sides of the parallelogram shown inFIG. 13A are formed of curved lines, and one diagonal line of this shapeis disposed to be coincident with one diagonal line of the IC card 11.

The shape shown in FIG. 13D is set so that two sides of the four sidesof the figure are formed of curved lines and the other two sides areformed of straight lines, and the curved lines are disposed to be closeto the corners of the IC card 11. The shape shown in FIG. 13E is formedof curved lines of two sides, and the line (diagonal line) connectingthe positions at which the curved lines are inverted (corresponding tothe corners) is disposed to be coincident with one diagonal line of theIC card 11. Further, the shape shown in FIG. 13F is an elliptical shape,and the major axis of the elliptical shape is disposed to be coincidentwith the diagonal line of the IC card 11.

The shape of the loop antenna 1 shown in FIG. 10 or FIG. 13 is set sothat when two IC cards 11 are stacked with being faced in the oppositedirections as described above, the corner portions (containing thecorner represented by a curved line) of the loop antenna 1 are notoverlapped.

In other words, the shape of the loop antenna 1 is set so that one ofcorner portions which confront each other with respect to the centerline of the IC card 11 (for example, the corner portion formed by thecurved line L3 and the linear portion L4 in FIG. 10) is far away fromthe center line and the other corner portion (for example, the cornerportion formed by the linear portion L4 and the curved line portion L5in FIG. 10) is closer to the center line.

Further, in other words, the shape of the loop antenna 1 is set so thatthe diagonal line of the IC card 11 is coincident with the lineconnecting two points of the loop antenna 1, one point being located atthe closest position to the corner portion of the IC card 11 and theother point being located at the confronting position (for example, inFIG. 10, the intersecting point between the curved line portion L3 andthe linear portion L4 and the intersecting point between the curved lineportion L5 and the linear portion L6).

By using the loop antenna 1 having any shape shown in FIG. 10 or FIG. 13as the antenna of an IC card 11, the reduction in reception sensitivitycan be suppressed even when two IC cards 11 are used while stacked, andthe same reception sensitivity as used when only one IC card is used canbe achieved. Further, the distortion of the signal to be received andprocessed can be suppressed. Further, even when plural IC cards 11 oftwo or more are used while stacked, the above-described concept iseffective, and the reduction in reception efficiency can be suppressedat maximum and the distortion can be suppressed even when the IC cardsare stacked in any way.

Accordingly, by using the present invention, such an anticollisionsystem that IC cards 11 are used while stacked can be easily fabricated.

In the foregoing description, the loop antenna 1 has four or six turns.However, the number of turns may be set to any value. Further, the loopantenna 1 is equipped to the IC card 11. However, the present inventionmay be applied to a card-like (planar) electronic device other than theIC card.

The term “system” in this specification means an overall apparatuscomprising plural devices, means or the like.

INDUSTRIAL APPLICABILITY

As described above, according to the electronic device of the presentinvention, when plural electronic devices are stacked so that at leastparts of the top sides thereof face each other or at least parts of theback sides thereof face each other, conductors constituting the loopantenna portions located in the neighborhood of the corners of theelectronic device having a substantially rectangular shape are notoverlapped with each other. Therefore, the reduction in receptionsensitivity can be suppressed, and the distortion of the signal receivedcan be suppressed.

1. A substantially-planar electronic device having a substantiallyrectangular shape, comprising: a loop antenna having at least two turnsof wiring that form a first arc-shaped portion and a second arc-shapedportion, wherein the first arc-shaped portion includes a first curvedportion and a first linear portion the second arc-shaped portionincludes a second curved portion and a second linear portion, wherein afirst corner of the loop antenna is formed by the first curved portionof the first arc-shaped portion meeting the second linear portion of thesecond arc-shaped portion, wherein a second corner of the loop antennais formed by the first linear portion of the first arc-shaped portionmeeting the second curved portion of the second arc-shaped portion,wherein the loop antenna is a first loop antenna and is oriented suchthat the first corner and the second corner of the first loop antennaare each in close proximity to at least one corner of the planarelectronic device, wherein the orientation of the first loop antennaprevents overlap of the first and second corner of the first loopantenna by corners of a second loop antenna, and wherein the second loopantenna is in another planar electronic device that at least partiallyoverlaps the planar electronic device of the first loop antenna.
 2. Theelectronic device as claimed in claim 1, wherein said loop antenna isshaped to have a parallelogram shape or elliptical shape as a basicshape.
 3. The electronic device as claimed in claim 1, wherein the basicshape of said loop antenna is constructed as a substantially annularshape by a combination of two straight lines and two curved lines whilethe two straight lines are disposed in parallel to each other.
 4. Theelectronic device as claimed in claim 1, wherein the basic shape of saidloop antenna is constructed as a substantially annular shape by acombination of two or four curved lines that are different in shape. 5.The substantially-planar electronic device as claimed in claim 1,wherein said device is a non-contact IC card.
 6. An information devicefor writing information to or reading information from asubstantially-planar electronic device having a substantiallyrectangular device, the information device comprising: an antenna; andreading writing means for reading information from or writinginformation to each of a plurality of electronic devices when saidplurality of electronic devices are partially overlapped with oneanother and each of said plurality of electronic devices has a loopantenna having at least two turns of wiring that form a first arc-shapedportion and a second arc-shaped portion, wherein the first arc-shapedportion includes a first curved portion and a first linear portion, thesecond arc-shaped portion includes a second curved portion and a secondlinear portion, wherein a first corner of the loop antenna is formed bythe first curved portion of the first arc-shaped portion meeting thesecond linear portion of the second arc-shaped portion, wherein a secondcorner of the loop antenna is formed by the first linear portion of thefirst arc-shaped portion meeting the second curved portion of the secondarc-shaped portion, wherein the loop antenna is a first loop antenna ofa first planar electronic device of the plurality of electronic devicesand is oriented such that the first corner and the second corner of thefirst loop antenna are each in close proximity to at least one corner ofthe planar electronic device, wherein the orientation of the first loopantenna prevents overlap of the first and second corner of the firstloop antenna by corners of a second loop antenna, and wherein the secondloop antenna is in a second planar electronic device of the plurality ofelectronic devices that at least partially overlaps the first planarelectronic device of the first loop antenna.
 7. An information readingmethod for reading information from a substantially-planar electronicdevice having a substantially rectangular device, the method comprisingthe steps of: emitting an electromagnetic wave to said electronicdevice; and reading information from the electronic device, saidelectronic device having a loop antenna comprised of at least two turnsof wiring that form a first arc-shaped portion and a second arc-shapedportion, wherein the first arc-shaped portion includes a first curvedportion and a first linear portion, the second arc-shaped portionincludes a second curved portion and a second linear portion, wherein afirst corner of the loop antenna is formed by the first curved portionof the first arc-shaped portion meeting the second linear portion of thesecond arc-shaped portion, wherein a second corner of the loop antennais formed by the first linear portion of the first arc-shaped portionmeeting the second curved portion of the second arc-shaped portion,wherein the loop antenna is a first loop antenna and is oriented suchthat the first corner and the second corner of the first loop antennaare each in close proximity to at least one corner of the electronicdevice, wherein the orientation of the first loop antenna preventsoverlap of the first and second corner of the first loop antenna bycorners of a second loop antenna, and wherein the second loop antenna isin another planar electronic device that at least partially overlaps theplanar electronic device of the first loop antenna.
 8. Asubstantially-planar electronic device having a substantiallyrectangular shape, comprising: a loop antenna having at least two turnsof wiring that form a first side and a second side, said first sideincludes a first linear portion and a first arc-shaped portion and thesecond side includes a second linear portion and a second arc-shapedportion.
 9. The electronic device of claim 8, wherein the firstarc-shaped portion meets the second linear portion at a first corner ofthe loop antenna, and the second arc-shaped portion meets the firstlinear portion at a second corner of the loop antenna.
 10. Theelectronic device of claim 9, wherein the loop antenna is a first loopantenna and is oriented such that the first corner and the second cornerof the first loop antenna are each in close proximity to at least onecorner of the electronic device, wherein the orientation of the firstloop antenna prevents overlap of the first and second corner of thefirst loop antenna by corners of a second loop antenna, and wherein thesecond loop antenna is in another planar electronic device that at leastpartially overlaps the planar electronic device of the first loopantenna.
 11. A planar electronic device having a substantiallyrectangular shape, comprising: a loop antenna having at least two turnsof wiring that form a polygonal shaped coil, said coil having a firstarc-shaped side and a second arc-shaped side, wherein said firstarc-shaped side and said second arc-shaped side meet to form a firstcorner of the loop antenna and a second corner of the loop antenna. 12.The electronic device of claim 11, wherein the loop antenna is a firstloop antenna and is oriented such that the first corner and the secondcorner of the first loop antenna are each in close proximity to at leastone corner of the electronic device, wherein the orientation of thefirst loop antenna prevents overlap of the first and second corner ofthe first loop antenna by corners of a second loop antenna, and whereinthe second loop antenna is in another planar electronic device that atleast partially overlaps the planar electronic device of the first loopantenna.